The system magnesium oxide-germanium dioxide

The phase equilibrium diagram for the system MgO-GeO 2 has been determined by the quenching method. Three compounds are found in the system: MgO.GeO 2 , melting congruently at 1700+ or -20 degrees C; 2MgO.GeO 2 ; and 4MgO.GeO 2 , which dissociates at 1495+ or -1O degrees C, to 2MgO.GeO 2 and MgO. A region of 2-liquid immiscibility extends from 8 to 34 mole % of MgO. Optical and X-ray data are given for the compounds, including a new monoclinic polymorph of MgO.GeO 2 which is analogous to clinoenstatite (MgO.SiO 2 ). This polymorph, apparently stable above 1555 degrees C, inverts to the orthorhombic form (analogous to enstatite) with heating below that temperature. A protoenstatite phase was not observed, although a detailed study was not attempted. Important differences between the MgO-Geo 2 and MgO-SiO 2 systems are that no 4:1 silicate compound is known and that MgO.GeO 2 melts congruently at a much higher temperature than the incongruently melting metasilicate.